Being in Texas, I'm noticing my gas mileage is down substantially while i run the AC. I normally get city stop-and-go MPG around 28. Now I get 25. which is sad for such a small car.

But - I wonder this: does the AC usage (compressor) change substantially with different settings? I'm thinking it *could*. For example, on the lowest fan setting, I'd imagine that the evaporator gets cold faster from what the compressor is doing (less hot, humid air going over it) and it would signal the compressor to cycle off more often. On the highest fan setting, I imagine more heat is dumped into the evap and the compressor probably has to run longer/more often. And who knows about the recirc/fresh setting...

Anyone have knowledge/conjecture on this?

 

The compressor cycles on and off to maintain the evaporator coil temperature in a fixed range.

Air entering from the outside first passes through the evaporator coil and is cooled. If anything but coldest is selected, it is directed over the heater core to warm the cold, dehumidified air. So selecting a warmer temperature doesn't help. On old-fashioned aftermarket A/C the temperature is controlled by cycling the compressor off more instead of mixing warm air, but any factory A/C uses the mixing method.

A lower fan speed might help: less air is being drawn in so the compressor runs less to maintain the evaporator temperature.

Using recirculate might help: it is cooling already cool inside air, so the compressor runs less to maintain the evaporator temperature.

Either of these may not be detectable in MPG: the compressor tends to run a lot either way.

 

I live in Arizona and I have found the opposite to be true for my 2007 base. During the 10 months of Summer I tend to get better fuel efficiency when running my A/C as opposed to not or to rolling down the windows. Weirds me right the crap out. I only ever use the first setting for air flow and a few seconds after turning on the blower I'll hit the A/C button. A few seconds after that I'll switch from vent to recirculate. I hit the A/C button again at stop lights to turn it off because there isn't enough power to be running the A/C and start rolling from a stop. After I get moving again I'll hit the A/C button to turn it back on. This results in about a +2mpg over the Summer from ~30mpg to ~32mpg.

 

I took the same trip two days apart this week, first day without the AC, second day with the AC on. I normally get 38mpg+ on this drive and averaged about 37.5 the first trip. With the AC on, I was getting no more than 35 (and that was trying to be more economical knowing that I would get worse fuel economy.) On many days, I see as much as 3-5mpg difference between AC On and AC off. It definitely kills economy.

~SB

 

I noticed no difference with or without AC on highway driving, and maybe a 1-2mpg difference in city driving when I was in Texas


Want better gas mileage? increase the air pressure in your tires. If you are on the stocks, the steelies with Dunlops have a max of 40psi, and I ran 35psi when I was stock. Mild change to driving comfort, but seemed to have a nice effect on city mileage. Highway mileage was unnoticably different

 

This is my experience also in 3 years of daily driving ownership. Hot and humid Texas summers with A/C fan on 3 or 4 versus no A/C and all windows down. Fan on lower setting and/or windows up then the gap narrows.

Only one scenario I can think of that would give you better mpg with A/C on versus off. That would be someone that runs with vent selector in defrost/windshield mode not knowing that it runs the A/C compressor. Then with windows open causing excessive drag, especially at highway speeds that could lose a mpg or two versus windows up.

_

 

I live in 10 Months Of Summer (heh) Phoenix, AZ. '13 Fit Base, 5 MT. When I get off work around 3:30 PM, it's usually the hottest time of day. I park with front of car facing away from the sun, and use window shade for front window. Crack the windows a bit.

Anyhoo, start up and usually go to 4 on the A/C setting, and drive say a mile or so, then switch to recirculate. After a couple of miles on the freeway, I'm down to 2 on the setting, and stays that way all the way home. If I'm driving into the sun, sometimes I'll go back up to 3 and that helps a lot.

With mixed city / freeway driving, am getting 33-34 MPG. Very happy about that considering A/C is on most of the time. So far, am driving to work (6 AM) w/o the A/C on, but time will come when I'll turn on the A/C even at that time of morning.

I do try to take it easy driving, and that helps a bit too. For such a tiny engine, the A/C does pretty good, altho I hate that cycle it goes thru when it blows hot air. Keeping the vent closed helps with that.

Sorry to be long winded. It's interesting to read your comments.

Hello all y'all to you guys in Texas. Have family in College Station.

 

I never run the car with windows open. I have hearing aids and the air hitting them and outside noise is simply too great. My wife uses ac all the time so her hair does not muss. I start with fan on high and usually drop to 2 when things get better. I cannot compare to windows open.. I can compare to winter. It is no contest. I get 37.5-39 in the summer and 34-36 in the winter.

We just got an 07 sport and we get similar number for summer. Have not had it for a winter yet.